SAN ANTONIO — A federal judge Monday questioned the reach of a new Texas “sanctuary cities” law supported by the Trump administration but that four of the nation’s largest cities, some police chiefs and immigrant-rights groups are trying to stop taking effect in September.

Hundreds of protesters, waving flags and carrying signs that read “Stop Separation of Families,” packed the plaza outside a San Antonio courthouse where U.S. District Judge Orlando Garcia will decide whether Texas can carry out the law that President Donald Trump’s Justice Department says is in-line with its crackdown on immigration.

A daylong court hearing about the constitutionality of the law — the first hearing since Republican Gov. Greg Abbott signed the bill known as SB4 in May — ended without Garcia ruling whether he will let Texas enforce the law. He did not set a timetable for a decision.

The law allows police officers to question people about their immigration status during routine stops and threatens police chiefs and elected officials with jail time and removal from office if they don’t comply with federal immigration requests to detain immigrants in the country illegally.

The four largest cities in Texas — San Antonio, Austin, Houston and Dallas– are suing to block the measure and their attorneys told Garcia that his ruling could determine if other states to pursue copycat measures. Lawyers for the Texas attorney general’s office responded that the new law has less teeth than Arizona’s “Show Me Your Papers” measure in 2010 that the was partially struck down by the U.S. Supreme Court.

“I’ll suggest that what we had in Arizona was a far more aggressive piece of legislation,” said Darren McCarty, special county to the Texas attorney general.

Garcia pushed attorneys on both sides over how exactly the law would play out on the streets. Would an officer during a traffic stop question the immigration status of every passenger, or just the driver? What would happen if a rank-and-file police officer who determined that someone wasn’t in the country legally didn’t turn over that information to U.S. Immigrations and Customs Enforcement?

The answer to the second questions is that nothing would happen, said McCarty, but he went on to contend that a police chief or sheriff who told his officers not to ever press people about their immigration status would be in violation.

“Texas must know what they’re doing,” said Lee Gelernt, an attorney with the American Civil Liberties Union. “They’re setting up a system that incentivizes people to enforce immigration law to the maximum.”

The four Texas cities — all of which are among the top 15 in the nation in population — accuse the Republican-controlled Texas Legislature of passing a law that is unconstitutional, vague and would have a chilling effect on immigrant communities. Abbott has said only lawbreakers have anything to worry about.

The hearing revisited the racial tension that simmered in the Texas Capitol both before and after Abbott signed the law. Democratic state Rep. Ana Hernandez, who did not become a U.S. citizen until she was 18 years old, wiped away tears on the witness stand as she recalled Republican colleagues referring to people who are not citizens as “illegals” during debate over SB4.

Weeks later, on the final day of the legislative session, tensions boiled over when Republican state Rep. Matt Rinaldi told Democrats that he had called federal immigration agents on protesters in the Capitol who held signs saying they were illegally in the country. One Democratic legislator admitted pushing Rinaldi, who responded by telling one Democrat that he would “shoot him in self-defence.”

The Trump administration, like Texas, has made “sanctuary cities” a target since the beginning of the year. U.S. Attorney General Jeff Sessions has threatened to pull federal money from jurisdictions that hinder communication between local police and immigration authorities and praised Texas last week for passing the law.